Two major energy suppliers are being queried by regulator Ofgem amid allegations of charging their customers too much.
The energy providers, who have not been named, are being probed for charging different prices for energy based on postcodes. There are also concerns that customers paying by cash, cheque and prepayment meters being charged over the odds.
It is believed that both energy suppliers will be revealed if an official investigation is launched.
Sarah Harrison of Ofgem commented: "We do have concerns over some premiums and have made it clear to the two suppliers concerned that we will take action if the differentials cannot be justified."
New regulations introduced in last year stipulate that any differences between tariffs must be down to differences in wholesale energy costs to the supplier and there should be no "undue price discrimination".
Moreover, new rules to be implemented this month will force energy suppliers to make their bills much clearer and state exactly how much energy each household is consuming, which will make it easier for consumers to compare energy deals to make sure they are receiving good value for money.
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